1. Field of the Invention
The present invention relates to apparatus for collecting fluid leakage that by-passes the stem seals on a rotary valve and, in particular, to actuator mounting apparatus for directly coupling a ball valve stem to a rotary actuator wherein the fluid leakage that by-passes the valve stem seals is collected therein.
2. Description of the Invention Background
The Environmental Protection Agency ("EPA") has recently estimated that more than 2.7 billion pounds of toxic air pollutants are emitted into the atmosphere every year. The EPA further estimates that the effects of these pollutants on the public health range from 1,000 to 3,000 additional cancer deaths annually.
Those studies and others like them, have helped to heighten the public's awareness and concern over pollution and its effects on the population and environment. Indeed, one need only open any industrial trade journal or major newspaper to appreciate the ever-increasing environmental legislation and public pressure being imposed upon industry to control pollution. For example, the Clean Air Act Amendments of 1990 have increased the number of regulated air pollutants from 7 to 189. Those amendments further require that industrial plants identified as being sources of such pollutants must install the best available pollution control devices to reduce their emissions to acceptable levels.
An important aspect of pollution control is centered around the elimination of fugitive emissions. Fugitive emissions is a term of art that refers to the leakage of liquid or gaseous process fluid from equipment such as valves, pumps and connectors. Although fugitive emissions emanating from a single valve or pump tend to be relatively small and sporadic, the large number of valves, pumps and connectors in most plants makes them a significant contributor to pollution.
Typically, the greater the majority of valve fugitive emissions tend to emanate from the valve stem area. Therefore, in the face of this burgeoning legislation, various valves and actuator connector apparatuses have been developed for detecting and collecting fugitive emissions that by-pass the valve stem seals. For example, U.S. Pat. No. 4,972,867 discloses a valve stem seal leak protection and detection apparatus that is adapted to detect and collect fugitive emissions that have by-passed the primary or first valve stem seal. That device comprises a stem extension member that is surrounded by a fluid collection and detection chamber that is connected to the upper portion of the valve. Secondary seals are provided on the outboard end of the chamber to prevent leakage around the stem extension member. However, the fugitive fluid that manages to by-pass the secondary stem extension seals is permitted to enter the environment with no warning.
In addition, that device has the distinct disadvantage of amplifying the amount of leakage permitted to by-pass the primary stem seal as a result of seal wear and failure. More specifically, as the distance between the primary stem seal and the point where the valve stem engages the rotary actuator is increased, the resulting moment acting on the primary seal is also increased which tends to further stress the primary stem seal. Therefore, it is desirable to keep the distance between the rotary actuator and the stem seals to a minimum to reduce the stress imposed on the stem seals and thereby increase the life of the seals. That aspect of actuator-to-valve attachment becomes even more critical when using ball valves, which are notorious for leaking around the stem seals.
There exists a wide variety of apparatuses for attaching a rotary actuator to a rotary controlled valve. For example, shaft-to-stem coupling devices have been used to connect the valve stem to a rotary output shaft of an actuator. That coupling method, however, increases the distance between the stem seals and the actuator and thus increases the amount of stress applied to the stem seals. Such devices not only increase the effective distance between the stem seals and the actuator, but also impact additional stress on the stem if the valve stem and the rotary output shaft are non in perfect alignment. Often times, due to the particular location of the valve, it becomes impossible to accurately determine whether the valve stem is in perfect axial alignment with the rotary output shaft of the actuator. Also, those coupling devices do not address the problem of detecting and collecting fugitive emissions resulting from stem seal deterioration and wear.
Other valve coupling apparatuses have addressed the problem of closely coupling a rotary actuator to a rotary controlled ball valve without the use of stem-to-shaft coupling devices. For example, the devices disclosed in U.S. Pat. No. 4,719,939 and U.S. Pat. No. 4,887,634 provide a means for closely coupling a rotary actuator to a valve stem without the use of a separate stem-to-shaft coupler. In those devices, the actuator is attached to the valve by a bracket plate which coaxially aligns the valve shaft with a drive socket located in the actuator. Those devices, however, provide no means for detecting or collecting the fugitive emissions that by-pass the stem seals before they reach the surrounding environment.
Thus, the need exists for an apparatus adapted to closely couple a rotary actuator to a rotary controlled valve while also providing a means for detecting and collecting fugitive emissions that by-pass the valve stem seals without creating a condition which allows a greater amount of fugitive liquid to by-pass the stem seals.